Electric safety limit switch



J. S. TOWNSEND luly em'ze." 1,591,249

ELECTRIC SAFETY LIMIT SWITH Filed Nov.' 15, 1920 3 Shuts-Sheet 1-IIIIII. v Illllll llll III IIIIII llll lllll July @1 26. 1,591,249

' J. 5. TOWNSEND ELECTRIC SAFETY mun swn'cn 1 Filed av. 15, 1920 sSheets-Sheet 2 July 6 1926.

J. s. TOWN$END ELECTRIC SAFETY LIMIT SWITCH Filed Nov. 15, 1920 3Sheets-Sheet a Patented July 6, 1926. I

Li; A

JOHN s. mownsmib, miHARVEY;uni-tiers; AssIGNoR To wnimme eoiefiorm'rion,or

HARVEY; rumors, A ooRPoRA'i Iorf oEiLLINoIsQ EL CTRIC" SAFETY L nnswr'i'oii.

This inventior is a safetyllirhit' switeh for Lise in e l'licientlystopplng any niechanism inovecl at high speed by' electrically propelledepperetus. While its application may be very general ,to devices havingthe same sort of mechanismthe invention Was primarily made for use inconnection with eleotrio trai eliiig Cranes and willtherefore bedesciibed in jeennection with sueh'hiaeh enisni. Y

it building equipped-With a travelingcrane,

movable horieontelly at a: certain given height} the efieetive usefulpart of the ca-v paoity oi the building; is the part; located belowthehigliest point to which the-lowest part of the hook or other movingp'artpf the crane caiijbe sz fely elevatecll .For this reason cranebuilders always strive to 1 so eoristruet the device that'the hook-andettechecl parts czin be moved to the highes't of i iithe bui ldiligfifltis also 7 Well understood the-tin the use ofe high SPQCl Lorene when thehook is" elevated at "high speed and the poweris shut ofl" the book mustneeessa point ithout danger to the crane mechan'is iir 'lhe object ofthis invention is to rproi icle enesitohietie meehenism which will outoff the current, controlling the hook,- at a poi-n15 eonsisterit-vi ithhigh '1 speed operation I of the" machi eencl to provide a manuallyeontrolletl meehan sm, by WhlClL oilly .L ncler the operators constantpersonal control the power maybe thrloiv n inageinyinr order to l permitfurther elevation oi the hook and attached parts, i113 to vanotherpredetermined point beyoiicl whieh the current is absolute- 1ytlii ciifiioff arid kept. off so thzttthehook meme by possibility proceedfurther, rm-i, thus clzlirilge the Crane mechanism;

The invention ooiisists in mechanismffor ettailiirigthe foregoingobjects which can be sceinparatively easily constructed and appl-iecl tomechanism requiring-it, which is perfectly positive and effieient inoperation aiicl isiiot liable to get out of Omen More par icularly theinv 'ehtion consists in r g titres and details of construction whichWill s1 .t-Q.

e 11, re tullyset forth int-be speeifisetion "7 S4, 7, V

A plication 'filfed, November It is .Well ontlerstootlii-n the t eirtthat in H rily' travelfe considerable V I -clistanee'upivardbeforethebrakes, or other sto -ping devices aet eii ectively, while on Y theotherhand, a slow moving hook might be safely stopped at considerably higher.15, 1920. sen- 1 1%.. merge;

numerals designate th the several views 1+:

e same parts thruout V ferr ed; form,

e;nclv vi eiv of a trolley pertially in iseetioni fillListrati-iig (hieform o f-t'he riieehzuii'sin oi .thisihvention ac ti zil eppilieeti-'Figure'3 is an liel' View alien (lithe ofFigiiije J2, certel parts,being veiit away.

Figure l is eiijeiicl iiieii" ofvtli-e switch iiieeheriism which is'shofiri diegra iiiiriati c elljiiiri Figure 1..

side View of the m chanism n er gure Vseet oir. Figure 6 1s a tliatpzlrtof the iaheoliziiiisi i which iwhieh is aiiidu a.

of Figure G'shdwing III eiiisrii eoirir noii t o the striietiires ofboth Fig iirs 5 and 6 In" Figure 1- the Winding; (liiiih, I0 is sheen,

I {to the mete shift 11", dr iveii;

, Referringto the clrziwings iri which 131;

Ill-gore lis e cliagremme-tie-"YieWof inec h .a-111s111; l-ll ustretlngthis IHYEfilJlOil iii its preright l; eertei i parts sheen in S6611 We qie lf ii-b o s 1 i i di- Y fiecl ZOnStI'HQtlOH Of the SWlftQll meehar smused in the dev ce of; Flgures 2 1 F'gure 211's ess cle viewofecraneencl i ,e fi l fie? thri l n 'ately the center of Figure e, but irpleee e egmmmeeau ceneeetee; by 1 i a .eorivei tionel rem of eleet'r'iee ror-101516,,

preview vwith siiiteble 'w'viriiig-lsof eoriventiomil leading toeiiisriiprovided with the ps ial oonventioiiel resistance 21 and in the casehere illustr'eitecl-,siiitebly eoiiiiected to ipair of normally opensw'itehes eoinmoiily celled alternating cu'i'ireiit is used and r is.

applied to the device frame suitable source etthegioi nts 2 8 v 11i: theplrys'icl meeher ism appliee' to ii traveling. zine,'insi1letors. .?i()

are applied at lili iell for the cr 'a iebmdge rmcl thet em t ef thetwangmeehen sm; at

eorit iotor' and s'iiigl'e rriernij l ly opercited switch 5% allofoonventional form 1 11-.

the lest of the'insulators is applied tofand 1 One end of carried by thecrane bridgeinconventional manner whereas the other parts of thewir-ving system are located at some other con- ,venient point, usually attheopeiating station, on the crane bridge. 1 e i In connection wlth theforegoing conven- .tional mechanism a special stop and switch mechanismis. applied for operation'by the crane hook block 32, which isconventionally suspended from the drum 10 by a hoisting rope In thecase'illustrated in Figure 1, block 32 does the mechanical portion ofthe stopping-by engaging a transversely'd1s-' posed rope 36, passing asshown betweenthe ropes 84., sothat the block cannot fail,'in its upwardtravel, regardless of its lateral swinging movement, to' engage thisrope 36.

while the'opposite end portion PP Q 5 after passing over suitable pulofthe rope,

ley l- 0, is wound around finally secured at one poi'it onthecircumfercnce of a wneel 42, carried by shaft 46 suitably mounted to2 leys 54. and 56.

' 7 Switch 24 is so' 'connectedin drive pinion 48, which in turn, ,thrua gear '50actuates shaft 52. A spring la connected to hub and to a fixedsupport i7, is

adapted to move the wheel and attached parts contrary to the pull ofrope .36. Mounted on this shaft 52 which is common to both of the switchmechanisms heretofore referred to, are two parallel segmental'puh remainin such engagement or contact during a. much longer portion of theIarcof travel of shaft'52r Both pulleys 54; and 56 are so positioned andarranged that'there is asubstantial portion of the arc of travel ofshaft 52 during which there is no contact with the adjacent switchpoints on either one of thee pulleys. Contact is so connectedinto thewiring circuit 18 thru a wire 66 that whenever block 32 strikes rope 36and thus ultimately rotates shaft 52 to the point where surface 58 ofpulley 5st is disen gagedfrom contact 60, magnet 26'is deenergized thusallowing the spring 22 to open connector 22 and thus throw off thecurrent from .motor 16 and stop the powerful elevation ofthe hookbloclr32.

therope is fastened to a fixed The pulleys 545 and 56ers the circuitthat when it'is manually closed, magnet 26 is operated, even thomembers58Iand 60 may will continueas long asswitch 2&remains closed; except ashereafter provided.

The relatively long circumferential 0011- tact surface is sopositionedand connected into the circuit thru wire .701 leading from contact tl lthat switch 24 can operate asQdescribed in the last sentence so long asmenr.

bore 64- remain in engagement with surface 62 but that when block 32*movs rope 36.11pward sufficiently so that'shaft 52 rotates far surface 62,the circuitiwhich switch 24' controls is in fact broken with the resultthat the operator holding switch 2% closed is no longer effective andcontactor 22 automatically opens as heretoforedescribed;thusp'erinanently preventing any further upward movement ofthe hook under thepower ofmotorlfi.

In actual practice the pulleys 5 tand56 are. so proportioned andpositioned that when block 32 engages rope 86 it causes the enough tomove contacts 6 1 as froin'contact breaking or opening of contact'58-60at apoint or timevinthe unwardtravel of L D an a e 1 clock e2where 1i itis moving at high speed.

ithas sinncient space within which to travel upwardso that the'brake andother" niechanism can stop it beforc 1t actuallyengages and therebyinjures the cranemechanism and that if the operator'maintains his hold 7on switch2 l the contact at62+67l will-not;

nism as it can possibly go withsafety at any speed, beyond which itcannot be moved further. In actual practice the operator is not supposedto close switch 24 when the crane is working at high speed until theblock has been automaticallystopped by breaking contact mechanism 586()and he' thereafter sees that the momentum upward of the block isnotgoing to carry it high enough. i V is working very slowly he may closeswitch 2% at or before the time contact 58 60 is broken and maintain ituntil switch opens. This does away with the temptatiom not to saynecessity, of operators of ordinary cranes having only 'a safety limitswitchat the level at which switch 58- -60 operates to run the load upat high speed in order to make it carry up by momentum to the upperlimit of travel, viz.: with this invention the operator can operateslowly all the way up and be sure of gettingthe load up to the maximumpoint without subjecthe broken as described'until the hook lock .82 hastraveled as near toithe cranemecha On the otherhand, the crane,

I when block move 1 36 upward to manipulate the mechanism as described,the pull of rope 36 compresses spring 44 whichreturns thepartsto-normal' position just as soon as the crane operator manipulates thedevice to cause block 32 to start to descend.

' Thecontroll'er mechanism 20- is of'abs'olutely standardconventionalform and the switch devices herein provided are only conwhich the 'ope reaches after. passing-over suitably disposed pulleys 80.Weight 78 is nected into it on its side which'isusedin'the the variousswitch devices entering intofthis' invention as described; v c

In the modified form of construction shown in Figures 2, '3' and 6 thespring 44 is dispensed with and its place istaken by a rope and weightmechanism. In this modi- Vfied construction the wheel 42wiil be designated as 72. To a suitable pointin its circumference a rope 7 4 issecured intermediate 7 of its ends so that it hasone free end carrying arelatively small weight 76 and its other end carrying a relatively largeweight 78,

perforated or otherwise provided with guides thru which ropes passtoinsure the; weight 78 following tlie swinging movement of block 32. Inthe construction of Figures 2 and 8 weight 7 8 1S enough heavier thanweight 76 so that when both. weightsv have controlof the 'pulley,'weight78 predomivnates and thereby: holds. the. switch mechanisnifin theposition of Figure 1, that is-to say in the same position, against stopmechanism '82 inwhich-the. parts are heldv by spring 44. Vhen, however,block device 32 ascends far enough to engageand' lift weight 7 78-,weight '76 is thrown incontrol with the result that: it moves the parts:in the same manner in which they are moved in the other constructionwhen. block a 32 moves "upward and pulls on rope 36'.

This weight mechanism form oi -device: has

the advantage of doing away with thespring and thus avoiding whatinighthappenif the spring broke or'otherwisefailed to operate:

It hardly seems necessary to describe the conventional form of craneshown in which the main crane girder 86 carrying the wheels 88 on whichthe trolley 90 hearing the crane mechanism described travels in theordinary manner. The main operating switch devices described areenclosed in a conventional form of box 92 mounted on the trolley inconvenient position for operation;

Having thus'described my invention what I claimas new and desiretosecure by Let icrsfatent is i v 1 In a, power mechanisms moving"merry- Ina power mechanism, ber, electrically operated, means propellingshaftymean' partially rota,

her, power meanspropelling it, 'two' power.

cut off devices, automaticallyoperatable insuccession by themovingmemberto, provided the power 18 on,,cut it off and norm-al-.

vly inoperativemechanism, vrendered operative by constant manualholding, in connection with: the:- second cut oil mechanism,

adaptedwhileso manually operated to 'rea store the 'pov've'r to thepropelling mechanism trom the timeth-efirstcut off operates until thesecond cutoiii itself operates.

52. In a power mechanism, a moving'meniit, twopower-cut oil"devices,automatically opera-tablein succession by the moving inemher to,providedthe power is on, cut it off and normally inoperative mechanismrendered opera-bleby constantmanual holding,

in connection with the second i cut oli mecha;

nism, adapted while so' manually-operated to restore'the power to thepropelling mechanism fronrthevtime the first cut oii operates until thesecond-cut oil itself operates;

13-. In a poWerniechanism, a movingmem}v s o0 henpower-"means propellingit, two power cut ofi"- device's automatically operatable 1'11 holy,electrical-lymperated means propelling succession by the" moving memberto, pro

v'i-d'ed the power is on,'cut it off and normally inoperative mechanismrendered operative by constant-manual holding, in connection with. thesecond cut oii mechanism, adapted while so manuallyoperatedto restorethe power to the propellingmechanism from the time-thefirst cut off opert until the s econ 1 Cut Off s l "op fates; a e

a moving me'mit, two power cutoli devices automatically- :operata'blein: succession -by the moving ,member to, provided the power is on, cutit off and normally inoperative mechanism rendered operative by constantmanual holding, in connection with-the secondcut operated to' restorethe power to the propel"- ling'niechanismfrom the time the first out offoperates'until; the second cut ofi itself operates. v

5: In mechanism of the class described, a movable member, electricallyoperated mechanismfor propelling themoving member, fan autdmafilcswitfih, operated by the moving member at' a predetermined point in itsoti mechanism, j adapted while somanually travelitocut-off the currentfrom the operat- 7 ing mechanism, -a normally" open switch closable byconstant manual holding,adaptedrwhen soclosedto restore" said current,and means o'peratable at a more distant point in -the travel olfthemoving member finally cuttingofl the current.

V 6'. Ina'deviceof the kind described, a moving member, an Veletric'circuited power mechanism normally moving said member, a

bY WhZ LClI the movingmember I 5 allel segmental cont-act members, ofdifferent circumferential lengths, on the shaft, a con-- tactor in theelectric circuit adapted to CQIL trol the power, a contact memberopposite the shorter segmental contact adapted when disengaged from thesegment to cause the contactor' to shut off the power, a manuallyoperated switch in a circuit arrangedto restore the power so shut offand contact members, engageable with the longer segmental contact on theshaft so connected into the last mentionedcircuit that so long as thesegment remains in position to maintain such contact, and said manuallyoperated switch is ope'rated,the efiect of said switch action operatedby the shorter segment is negatived; V

7. In mechanism of the classdescribed, a' moving load controlled member,an electric c ircuited power -mechanism normally moving said controlledmember, a movable switch 'm'ember," means by which at a predeterminedtime in the travel of said ccontrolled member it movesthe switch member,

to maintain 'said circuit closed, the effect of the ,power shut off bythe shorter circuitcomp'leting member is negatived.

, 8. In mechanism of the class described, a moving load controlledmember, an electric circuited power mechanisn normally mov ing saidcontrolled member, a movable switch member, means by which at apredetermined time in the travel of said controlled member it moves theswitch member a pair of separated, parallel circuit-completing membersof different operating lengths on the switch member, a contactor in theelectric circuit adapted to control the power,

' a cooperating member opposite the shorter circuit completing member onthe switch member adapted when disengaged therefrom topermit thecontactor to shut off 1the power, a manually controlled switch in a crcuit arranged to restore. the power'so' shut olf and anothercooperating member cooperating with the'longer of saidcircuit-completing members on the switch member, so connected into thelastmentioned circuit that so long as the longer circuit-completinmember remains in position to maintain eai -the opposite direction.

circuit closed and said switch is operated,;.

the effect of the power shut off by the shorter circuit-completingmember is negatived.

9. In mechanism of the class described, a

moving load controlled mcmber,an electric oircuited power mechanismnormally moving said controlled 'member, a movable switch member, meansby which at a predetermined time in the travel of saidcontrolled memberit'moves the switch mem-r her, a pair'of separated, parallelcircuitcompleting members of different operating lengths on the switchmember, a contactor in the electric circuit adapted to control thepower, a cooperating member opposite the shorter circuit-completingmember on the switch member adapted when disengaged therefrom to permitthe contactor to shut off the power, a circuit arra'ngedto restore thepower so shutoff and another cooperat said circuit-completing members onthe switch member, so connected into the last mentioned circuit that solong as the longer circuit-completing member remains ini-positionto'maintain said circuit closed, the effect of the power shut off by theshorter circuitcompleting memberis negatived, and means resisting'saidmovement of the switch member, returning said switch to originalposition when the controlled member moves in 10. In mechanism of movingload controlled member, an electric circuited power mechanism normallymov-I ing said controlled .member, a movable switch member, meansbywhich at a predetermined time inrthe travel of said controlled member,it moves the switch meming member'coo'perating with the longer oftheclass described, a 7

her, a pair of separated, parallel circiiitcompleting members ofdifferent operating lengths on the switch member, a contactor in theelectric circuit adapted to control the power, a cooperating memberopposite the shorter circnit-completing membei on the switch memberadapted when disengaged therefrom to permit the contactor to shut offthe power, a manually controlled switch in acircuit arranged to restorethe power completing members on'the switch member, so connected into thelastimentioned circuit that so long as the longer circuit-completingmember remains in position to maintainsaid circuit closed and saidswitch is operated, the effect of the power shut off by the shorter.circuit-completing member is negatived, and means resisting saidmovement of the'switch member, returning said switch to" originalposition when controlled member moves in theopp'osite direction.

11. In mechanism of theclass described,

a mevablexswitch member, means automati I so shut off and anothercooperating member cooperating with thelonger of said circuittion, apair of separated, circuit-completing.

' members of different lengths carried by the switch member, stationarycooperating mem- .;bers opposite said circuit-completing members adaptedwhen the switch is moved to open circuits in which they are respectivelyincluded during periods oftime determinedby the lengths ofthe respectivecircuit com-' pleting devices on the movable switch.

a rotatable switch member, means automatically restoring said switch toinitial posi- .:'sWitch.

12. In mechanism of theclass described,

scribed my name. r 1 v p a Y JOHN S. TOWNSEND,

members of different lengths carried by the tion, a pair of separated,circuit-completing J I switch member, and stationary cooperating membersopposite said circuit-completing members adapted when the switch ismoved tively included during periods of time decircuit completingdevices on the movable In witness whereof,

1 toopen circuitsin which they are respecc I have hereunto sub:

